With the rapid development of mobile communications, a power amplification circuit is more and more widely applied to a base station and a mobile terminal, cascaded application occasions are increasing, and requirements for efficiency and linear indexes are increasingly high. How to meet a linear requirement of an amplification circuit and continuously improve the efficiency has become a new challenge for a design of a power amplifier.
As a current industry mainstream device, a Laterally Diffused Metal Oxide Semiconductor (LDMOS) field-effect tube has been widely applied by virtue of good performance indexes, reliable stability and other advantages. One of working characteristics of the LDMOS field-effect tube is that a gain characteristic of an LDMOS will change along with a change of a static working current, that is, a gain shape depends on the static working current of the LDMOS field-effect tube. FIG. 1 and FIG. 2 are typical gain curves of LDMOS field-effect tubes in different power levels.
From the gain curves of the LDMOS field-effect tubes, it can be seen that the static working current of each LDMOS field-effect tube remarkably affects the amplification characteristic of each LDMOS field-effect tube, particularly, when an input power is relatively low. Meanwhile, the characteristic does not change due to a difference of the power levels of the LDMOS field-effect tubes.
A cascaded LDMOS field-effect tube is adopted in the current industry to achieve power amplification, and each stage of LDMOS field-effect tube is set in accordance with a recommended static working current so as to guarantee a consistency of large and small signal gains of all stages of LDMOS field-effect tubes. Although this mode can guarantee a good linearity of a cascaded amplifier, an efficiency of an entire link is not high.